SIMS is a different type of analytical technique from many others (such as PIXE or EMPA). The important difference here is that there exists no theory to predict the count rate one will measure for some element in a given geological (or other) matrix at a given concentration. In some cases, for example, simply adding a few percent of iron to a sample will change dramatically the count rate for an element. From the first applications of SIMS to earth sciences, few decades ago, there has been the problem of converting the measured signal intensity to concentrations. At best, a standard of the same major-element composition as the unknown could be used to calibrate the signal, but many times such a material is not available. The question then arises: "How close must a standard be to the chemistry and structure of the unknown material?" The intimate knowledge of how secondary ion intensities vary with abundance and sample chemistry is essential for anyone operating a SIMS lab. in the earth sciences. Interferences in the secondary-ion mass spectra represent a further inherent drawback of SIMS, which has hampered its direct use in complex matrixes such as minerals or rocks. In many cases, the isobars (molecular, oxide, doubly- or multiply charged ions, etc..) contribute for the most part to the secondary-ion currents at some mass number. The removal or correction of such interferences represents a pre-requisite to the application of quantitative SIMS. Since 1988, birth date of the SIMS lab. at CNR- Pavia (Italy) our efforts have been addressed to overcome the limitations inherent the SIMS technique in order to obtain precise and accurate results in the elemental analysis of REE, HFSE, LILE in silicate minerals and glasses (as melt inclusions and interstitial glasses) in a variety of rocks. In case of light elements, the adoption of the "energy filtering" technique has revealed the key both to reduce matrix effects and improve measurement reproducibility. Our SIMS procedure has allowed for the quantitative analysis of Li, Be and B in a variety of geological samples by means of a small number of calibration standards and mathematical corrections to the ion yield. Such a procedure has been extended to the volatile elements H, F, Cl for which it is possible now to face the quantitative analysis over a wide concentration range in a variety of silicate and non-silicate samples. Our ion microprobe Cameca ims 4f has been recently used to investigate REE, actinides, and light elements in complex matrixes (hellandite, britholite, etc..) of interest in earth and material sciences. The capabilities of SIMS in accurate quantification of light (Z <6) and heavy (Z >57) elements as trace, minor and major constituents (?REE(ox) up to ~70 wt % in britholite) have been demonstrated. Examples of our SIMS applications in the earth sciences will be shown at the Symposium.
Applications of SIMS to the elemental analysis in geological samples
OTTOLINI Luisa
2007
Abstract
SIMS is a different type of analytical technique from many others (such as PIXE or EMPA). The important difference here is that there exists no theory to predict the count rate one will measure for some element in a given geological (or other) matrix at a given concentration. In some cases, for example, simply adding a few percent of iron to a sample will change dramatically the count rate for an element. From the first applications of SIMS to earth sciences, few decades ago, there has been the problem of converting the measured signal intensity to concentrations. At best, a standard of the same major-element composition as the unknown could be used to calibrate the signal, but many times such a material is not available. The question then arises: "How close must a standard be to the chemistry and structure of the unknown material?" The intimate knowledge of how secondary ion intensities vary with abundance and sample chemistry is essential for anyone operating a SIMS lab. in the earth sciences. Interferences in the secondary-ion mass spectra represent a further inherent drawback of SIMS, which has hampered its direct use in complex matrixes such as minerals or rocks. In many cases, the isobars (molecular, oxide, doubly- or multiply charged ions, etc..) contribute for the most part to the secondary-ion currents at some mass number. The removal or correction of such interferences represents a pre-requisite to the application of quantitative SIMS. Since 1988, birth date of the SIMS lab. at CNR- Pavia (Italy) our efforts have been addressed to overcome the limitations inherent the SIMS technique in order to obtain precise and accurate results in the elemental analysis of REE, HFSE, LILE in silicate minerals and glasses (as melt inclusions and interstitial glasses) in a variety of rocks. In case of light elements, the adoption of the "energy filtering" technique has revealed the key both to reduce matrix effects and improve measurement reproducibility. Our SIMS procedure has allowed for the quantitative analysis of Li, Be and B in a variety of geological samples by means of a small number of calibration standards and mathematical corrections to the ion yield. Such a procedure has been extended to the volatile elements H, F, Cl for which it is possible now to face the quantitative analysis over a wide concentration range in a variety of silicate and non-silicate samples. Our ion microprobe Cameca ims 4f has been recently used to investigate REE, actinides, and light elements in complex matrixes (hellandite, britholite, etc..) of interest in earth and material sciences. The capabilities of SIMS in accurate quantification of light (Z <6) and heavy (Z >57) elements as trace, minor and major constituents (?REE(ox) up to ~70 wt % in britholite) have been demonstrated. Examples of our SIMS applications in the earth sciences will be shown at the Symposium.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
